Radio communication system, communication controller, and base station to transmit data with commom content with one or more other base stations

ABSTRACT

Each of two or more base stations notifies a communication controller of information on a first frequency band that the base station uses for radio communication. Based on the information on the first frequency bands acquired from the two or more base stations, the communication controller selects a second frequency band to be used by the two or more base stations to transmit the data with common content, and notifies the two or more base stations of information on the selected second frequency band. The two or more base stations transmit the data with common content based on the information on the second frequency band acquired from the communication controller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of InternationalApplication PCT/JP2010/069885 filed on Nov. 9, 2010 which designated theU.S., the entire contents of which are wholly incorporated herein byreference.

FIELD

The embodiments discussed herein are related to a radio communicationsystem, a communication controller, and a base station.

BACKGROUND

Currently, radio communication systems such as mobile phone systems andwireless LAN (Local Area Networks) are widely in use. In addition,active discussions on next generation radio communication technologyhave been continued in order to further increase the speed and capacityof radio communication. For example, the 3GPP (3rd GenerationPartnership Project), which is an international standards organization,has proposed a communication standard called LTE (Long Term Evolution)which allows data communication using a frequency band up to 20 MHz.Further, a communication standard called LTE-A (Long TermEvolution-Advanced) which allows data communication using up to five20-MHz carriers (that is, 100 MHz) has been proposed as a nextgeneration communication standard after the LTE standard.

In LTE and LTE-A, a data transmission scheme called MBSFN (MultimediaBroadcast multicast service Single Frequency Network) has been examined.In a radio communication system providing MBSFN transmission, one ormore MBSFN areas each including multiple base stations are formed. Themultiple base stations belonging to the same MBSFN area concurrentlytransmit data with the same content using the same frequency and thesame modulation scheme. Data transmitted using MBSFN is sometimesreferred to as the MBMS (Multimedia Broadcast Multicast Service) data. Amobile station combines MBMS data signals transmitted from multiple basestations, and demodulates and decodes the combined signal, which leadsto an improvement in reception quality of the MBMS data.

As for LTE, a proposed technique is directed to a base station operatingmultiple cells, which acquires capability information from a mobilestation in the case where frequency bands for data transmission andreception are different for different mobile stations, and determines atarget cell of the mobile station based on the capability information(see, for example, International Publication Pamphlet No. WO2008/023613). As for MBSFN, a technique has been proposed in which aserving cell selected from among cells in an MBSFN area and allocatingradio resources to a mobile station notifies the mobile station of afrequency at which MBMS services are provided (see, for example,Japanese Laid-open Patent Publication No. 2009-182944). Another proposedMBSFN technique is directed to a control apparatus called MCE(Multi-cell/multicast Coordination Entity) which collects, via basestations, reports on quality of MBMS services evaluated by mobilestations and allocates radio resources based on the collected reports(see, for example, Japanese Laid-open Patent Publication No.2009-246526).

In a radio communication system where multiple base stations maytransmit data with the same content at the same frequency, acommunication controller such as an MCE may select a frequency band usedfor transmitting the data with the same content and instruct the basestations to use the frequency band. On the other hand, the base stationsmay employ different frequency bandwidths, such as 10 MHz, 15 MHz, and20 MHz, for their radio communication. Further, the base stations mayoperate at different center frequencies with the various frequencybands.

As a result, what remains an issue is how the communication controllerselects the above-described frequency band used for transmitting thedata with the same content. Assume, for example, that the communicationcontroller selects a frequency band of 15 MHz for the transmission whilethere is a base station using a frequency band of only 10 MHz in theradio communication system. In this case, due to lack of radioresources, the base station is not able to transmit data for up to 5 MHzof the data with the same content. This may result in a decrease inreception quality at a radio receiver with respect to the data with thesame content transmitted from two or more base stations.

SUMMARY

According to an aspect of the embodiments to be discussed herein, thereis provided a radio communication system. This radio communicationsystem includes a communication control apparatus; a plurality of basestations; and a radio receiving apparatus, in which radio communicationsystem, two or more base stations among the plurality of base stationstransmit data with common content to the radio receiving apparatus at afrequency common to the two or more base stations, wherein each of thetwo or more base stations includes a first control unit for notifyingthe communication control apparatus of information on a first frequencyband that the base station uses for radio communication, and controllingtransmission of the data with common content based on information on asecond frequency band notified of by the communication controlapparatus, and the communication control apparatus includes a secondcontrol unit for selecting the second frequency band used to transmitthe data with common content based on the information on the firstfrequency bands notified of by the two or more base stations, and anotifying unit for notifying the two or more base stations of theinformation on the selected second frequency band.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a radio communication system according to a firstembodiment;

FIG. 2 illustrates a mobile communication system according to a secondembodiment;

FIG. 3 illustrates a configuration example of an MBSFN area;

FIG. 4 illustrates a structural example of a radio frame;

FIG. 5 illustrates a structural example of a subframe;

FIG. 6 illustrates a structural example of a symbol;

FIG. 7 illustrates a method of combining MBMS data signals;

FIG. 8 illustrates an example of how to set a frequency band;

FIG. 9 is a block diagram of an MCE;

FIG. 10 is a block diagram of a base station;

FIG. 11 is a block diagram of an MBSFN control unit of the base station;

FIG. 12 is a block diagram of a mobile station;

FIG. 13 is a flowchart illustrating band control exercised by the MCE;

FIG. 14 is a flowchart illustrating band control exercised by the basestation;

FIG. 15 is a flowchart illustrating band control exercised by the mobilestation;

FIG. 16 is a sequence diagram illustrating a flow of communicationaccording to the second embodiment;

FIG. 17 is a sequence diagram (continuing from FIG. 16) illustrating theflow of communication according to the second embodiment;

FIG. 18 illustrates a first example of how to set an MBSFN band;

FIG. 19 illustrates a second example of how to set the MBSFN band;

FIG. 20 is a block diagram illustrating a first modification example ofan MCE according to a first modification;

FIG. 21 is a block diagram illustrating a second modification example ofan MCE according to a second modification;

FIG. 22 illustrates a configuration example of component carriers;

FIG. 23 is a block diagram of an MME; and

FIG. 24 is a sequence diagram illustrating a flow of communicationaccording to a third embodiment.

DESCRIPTION OF EMBODIMENTS

Several embodiments will be described below with reference to theaccompanying drawings.

First Embodiment

FIG. 1 illustrates a radio communication system according to a firstembodiment. The radio communication system of the first embodimentincludes a communication controller 10, multiple base stations includingbase stations 20 and 20 a, and a radio receiver 30. The communicationcontroller 10 is, for example, an MCE. The communication controller 10may be a device independent of the multiple base stations, or may beinstalled in at least one of the multiple base stations. The basestations 20 and 20 a transmit data with common content (for example,data with the same, or partially the same, content) to the radioreceiver 30 at a frequency common to both the base stations 20 and 20 a(for example, the same frequency). For example, the base stations 20 and20 a carry out MBSFN transmission. Note that the radio receiver 30 maybe a mobile or fixed radio communication device.

The communication controller 10 includes a control unit 11 and anotifying unit 12. The control unit 11 may acquire, from each of thebase stations 20 and 20 a, information on a frequency band that the basestation 20/20 a uses for radio communication with the radio receiver 30(first frequency band). The first frequency band of the base station 20may be different from that of the base station 20 a. Based on theacquired information on the first frequency bands, the control unit 11may select a frequency band to be used by the base stations 20 and 20 ato transmit data with common content (second frequency band). Thenotifying unit 12 may notify the base stations 20 and 20 a ofinformation on the second frequency band selected by the control unit11.

The base station 20 includes a transmitting unit 21 and a control unit22. Similarly to the base station 20, the base station 20 a alsoincludes a transmitting unit and a control unit. Under the control ofthe communication controller 10, the transmitting unit 21 may transmitdata with content common to data transmitted by the base station 20 a ata frequency in common with the base station 20 a. The control unit 22may notify the communication controller 10 of the information on thefirst frequency band of the base station 20, and acquire information onthe second frequency band from the communication controller 10. Thecontrol unit 22 controls data transmission of the transmitting unit 21based on the acquired information on the second frequency band. Forexample, the control unit 22 may map a data signal to the secondfrequency band. The control unit 22 may notify the radio receiver 30 ofthe information on the second frequency band.

The radio receiver 30 combines data signals transmitted by the basestations 20 and 20 a and extracts data from the combined data signal.The radio receiver 30 includes a control unit 31. When notified of theinformation on the second frequency band by the base station 20 (or 20a), the control unit 31 may control reception of data transmitted by thebase stations 20 and 20 a in a coordinated manner, based on theinformation on the second frequency band. For example, the control unit31 may control the data reception to extract the data signal in thenotified second frequency band.

The multiple base stations are capable of individually operating atsubstantially the same center frequency (alternatively, substantiallythe same maximum or minimum frequency) of their corresponding firstfrequency bands. The bandwidths of the first frequency bands employed bythe individual base stations may be different from one another. In thatcase, each of the base stations 20 and 20 a may notify the communicationcontroller 10 of information on the first frequency band, for example,information indicating a bandwidth of the first frequency band. Thecommunication controller 10 notifies the base stations 20 and 20 a ofinformation on the second frequency band, for example, informationindicating a bandwidth of the second frequency band.

Alternatively, the multiple base stations may operate at mutuallydifferent center frequencies of their first frequency bands. In thatcase, the information on the first frequency band notified of by each ofthe base stations 20 and 20 a may indicate the center frequency and thebandwidth of the first frequency band. The information on the secondfrequency band notified of by the communication controller 10 mayindicate the center frequency and the bandwidth of the second frequencyband. Note however that the way to designate the first and secondfrequency bands is not limited to the above-described method. Forexample, a frequency band likely to be used by the multiple basestations may be divided into multiple sub-ranges, to each of which anidentification symbol is assigned, so that the designation of theindividual first and second frequency bands is made using anidentification symbol corresponding to a sub-range to be used.

The second frequency band may be selected, for example, from a frequencyrange included in both the first frequency bands of the base stations 20and 20 a (i.e., a frequency range commonly used by the base stations 20and 20 a). The control unit 11 may select the whole of the commonfrequency range as the second frequency band. Alternatively, determiningthe common frequency range as an available frequency band, the controlunit 11 may select a part or the entire available frequency band inresponse to the status of the data transmission. Note that if there isno frequency range commonly used by all of two or more base stations fortransmitting data with common content, a frequency range commonly usedby the most base stations may be selected as the second frequency band.

The information on the first frequency band may be sent from each of thebase stations 20 and 20 a to the communication controller 10, forexample, when the base stations 20 and 20 a individually start theiroperation. In addition, if a change is made to the first frequency bandof the base station 20/20 a, the corresponding base station 20/20 anotifies the communication controller 10 of information on the changedfirst frequency band. Upon acquiring the information on the changedfirst frequency band, the control unit 11 may recalculate the secondfrequency band (or the frequency band available as the second frequencyband). In addition, the control unit 11 may carry out the recalculationwhen there is a change to the group of multiple base stations fortransmitting data with common content.

Assume, for example, that the base stations 20 and 20 a for transmittingdata with common content operate in the first frequency bands of 10 MHzand 20 MHz, respectively, but that the first frequency bands of the basestations 20 and 20 a have the same center frequency. The control unit 11may select 10 MHz, which is the smaller one of the bandwidths of thebase stations 20 and 20 a, as the bandwidth of the second frequency bandused to transmit the data with common content. This facilitates both thebase stations 20 and 20 a to reserve radio resources of 10 MHz used totransmit the data with common content. Note that when there is a changeto the first frequency band of the base station 20 or when the basestation 20 stops transmitting the data with common content, the controlunit 11 may recalculate the bandwidth of the second frequency band.

According to the radio communication system of the first embodiment,each of the base stations 20 and 20 a notifies the communicationcontroller 10 of information on the first frequency band that the basestation 20/20 a uses for radio communication. Based on the informationon the first frequency bands notified of by the individual base stations20 and 20 a, the communication controller 10 selects the secondfrequency band to be used by the base stations 20 and 20 a to transmitdata with common content. Subsequently, the communication controller 10notifies the base stations 20 and 20 a of information on the selectedsecond frequency band. Based on the notified information on the secondfrequency band, the base stations 20 and 20 a transmit the data withcommon content.

This allows the communication controller 10 to recognize settingstatuses of the first frequency bands of the base stations 20 and 20 aand, therefore, the communication controller 10 is able to designate anappropriate second frequency band for the base stations 20 and 20 a. Theappropriate designation of the second frequency band reduces thepossibility that the individual base stations 20 and 20 a will beincapable of transmitting part of data due to lack of radio resourcestherein. As a result, it is possible to reduce loss of data receptionquality at the radio receiver 30. In addition, as compared to the caseof selecting the second frequency band on the basis of using thesmallest possible bandwidth for the first frequency bands, the firstembodiment prevents the bandwidth of the second frequency band frombecoming excessively small and, thus, ensures the efficient use of radioresources of the base stations 20 and 20 a. Further, the communicationcontroller 10 is able to provide a dynamic response to a change made tothe first frequency band of the base station 20/20 a.

Note that the radio communication system of the first embodiment may beimplemented as an LTE or LTE-A system. Second and third embodimentsdescribed below are directed to examples of an LTE or LTE-A mobilecommunication system.

Second Embodiment

FIG. 2 illustrates a mobile communication system according to the secondembodiment. The mobile communication system of the second embodimentincludes an MCE 100; multiple base stations including base stations 200,200 a, and 200 b; a mobile station 300; an MME (Mobility ManagementEntity) 41; an MBMS gateway 42; and a SAE (System ArchitectureEvolution) gateway 43. The MCE 100 and the mobile station 300 areexamples of the communication controller 10 and the radio receiver 30,respectively, described above.

The MCE 100 is a communication controller for controlling MBSFNtransmission. The MCE 100 receives, from each of the base stations 200,200 a, and 200 b, a band notification indicating a frequency band usedby (or available for) the base station for radio communication, anddetermines a frequency band available for transmission of MBMS data. TheMCE 100 also receives an MBSFN request indicating a desired MBMS servicefrom the mobile station 300 via the base station 200, and schedulestransmission of MBMS data. Subsequently, the MCE 100 transmits, to thebase stations 200, 200 a, and 200 b and the MBMS gateway 42, MBSFNcontrol information indicating radio resources and a Modulation andCoding Scheme (MCS) to be used for the transmission of MBMS data.

The base stations 200, 200 a, and 200 b are radio communication devicesfor individually communicating via radio waves with the mobile station300. Each of the base stations 200, 200 a, and 200 b is connected to theMCE 100, the MME 41, the MBMS gateway 42, and the SAE gateway 43 via awired network. Each of the base stations 200, 200 a, and 200 b isconfigured to transfer dedicated data of the mobile station 300 betweenthe mobile station 300 and the SAE gateway 43. In addition, under thecontrol of the MCE 100, all the base stations 200, 200 a, and 200 bcarry out MBSFN transmission, in which MBMS data acquired from the MBMSgateway 42 is transmitted.

Note that the base stations 200, 200 a, and 200 b may use differentfrequency bands for the radio communication with the mobile station 300.The bandwidth of each of the frequency bands is selected, for example,from 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. In addition, thefrequency bands used by the base stations 200, 200 a, and 200 b may bedynamically changed during the operation. For example, each of the basestations 200, 200 a, and 200 b is configurable to operate in a frequencyband with a wider bandwidth during high traffic hours while operating ina frequency band with a narrower bandwidth during low traffic hours.

The mobile station 300 is a radio terminal, such as a mobile telephoneor a mobile information terminal, and communicates via radio waves withthe base stations 200, 200 a, and 200 b. The second embodiment isdirected to a case in which the mobile station 300 is connected to thebase station 200. The mobile station 300 transmits dedicated data to thebase station 200 in the uplink (UL), and receives dedicated data fromthe base station 200 in the downlink (DL). In addition, the mobilestation 300 receives MBMS data transmitted in the downlink by MBSFN. Themobile station 300 combines MBMS data signals concurrently transmittedby multiple base stations, including the base stations 200, 200 a, and200 b, at the same frequency, and demodulates and decodes the combinedsignal to extract the MBMS data.

The MME 41 is a communication controller for managing the mobility ofthe mobile station 300. The MME 41 communicates with the base stations200, 200 a, and 200 b to manage a serving cell of the mobile station300. The MBMS gateway 42 is a communication device for processing MBMSdata to be transmitted by MBSFN. Based on MBSFN control informationreceived from the MCE 100, the MBMS gateway 42 transmits MBMS data tothe base stations 200, 200 a, and 200 b. The SAE gateway 43 is acommunication device for processing dedicated data of the mobile station300. The SAE gateway 43 transmits dedicated data directed to the mobilestation 300 to the base station 200, and receives dedicated datatransmitted by the mobile station 300 from the base station 200.

Note that MBSFN operation is controlled by the stand-alone MCE 100according to the second embodiment. However, the function of the MCE 100may be implemented on at least one of the base stations 200, 200 a, and200 b. For example, a control device corresponding to the MCE 100 may beinstalled in the base station 200, which communicates with the basestations 200 a and 200 b to control MBSFN operation. Alternatively, thefunction of the MCE 100 may be implemented on a different communicationcontroller in the wired network, such as the MME 41.

FIG. 3 illustrates a configuration example of an MBSFN area. Within theMBSFN area, MBMS data transmission is synchronized by the control of theMCE 100. The MBSFN area includes 19 cells (cells #1 to #19) accordingthe example of FIG. 3.

Assume here that the mobile station 300 exists in cell #1, and that MBMSdata to be received by the mobile station 300 is transmitted in thecells #1 to #19 included in the single MBSFN area. In this case, themobile station 300 combines MBMS data signals of up to 19 cells, anddemodulates and decodes the combined signal, to thereby extract the MBMSdata. Note however that it is possible to prevent the MBMS data to bereceived by the mobile station 300 from being transmitted in some cellsof the MBSFN area. In addition, a single cell may belong to multipleMBSFN areas.

FIG. 4 illustrates a structural example of a radio frame. The radioframe as illustrated in FIG. 4 is transmitted between the base stations200, 200 a, and 200 b and the mobile station 300. Note however that thestructure of FIG. 4 is merely an example, and the structure of the radioframe is not limited to this example. According to the example, theradio frame with a duration of 10 ms includes 10 subframes (subframes #0to #9) each having a duration of 1 ms. Each subframe includes two slots,each with a duration of 0.5 ms. That is, the 10-ms radio frame includes20 slots (slots #0 to #19).

For management purposes, radio resources in the radio frame aresubdivided in the time and frequency directions. As a multiplexingaccess scheme, for example, OFDMA (Orthogonal Frequency DivisionMultiple Access) is used for the downlink, and SC-FDMA (Single-CarrierFrequency Division Multiple Access) or N×DFT-s-OFDM (N×Discrete FourierTransform spread Orthogonal Frequency Division Multiple Access) is usedfor the uplink. Each slot includes 7 or 6 symbols in the time direction.In each symbol, a guard interval called cyclic prefix (CP) is inserted.In the frequency direction, the radio frame includes multiple resourceblocks (RB), each of which includes multiple subcarriers. Radioresources defined in the time-frequency domain are assigned to eachchannel.

In a downlink radio frame, a Synchronization Channel (SCH) fortransmitting a synchronization signal is assigned to slots #0 and #10. APhysical Broadcast Channel (PBCH) for transmitting broadcast informationis assigned to slot #1. In slots #8 and #18, a Paging Channel (PCH),which is a transport channel used for paging the mobile station 300, ismapped to a Physical Downlink Shared Channel (PDSCH).

Note that a subframe for transmitting MBMS data (MBSFN subframe) isselected from subframes #1 to #3 and #6 to #8, to which none of the SCH,PBCH, and PCH is assigned.

FIG. 5 illustrates a structural example of a subframe. In the example ofFIG. 5, subframe #0 is a normal subframe, and subframe #1 is an MBSFNsubframe. The normal subframe includes 7×2 symbols with normal cyclicprefixes inserted thereinto while the MBSFN subframe includes 6×2symbols with extended cyclic prefixes inserted thereinto. In eachsubframe, plot signals called reference signals (RS) are transmitted.The reference signals are used to measure reception quality at themobile station 300. The reference signals in the normal subframe have adifferent signal sequence from that of the reference signals in theMBSFN subframe.

Although FIG. 5 depicts only one resource block in the frequencydirection to facilitate easy understanding, the radio frame actuallyincludes multiple resource blocks in the frequency direction. Forexample, in a frequency band of 1.4 MHz, 6 resource blocks are included;in a frequency band of 3 MHz, 15 resource blocks are included; in afrequency band of 5 MHz, 25 resource blocks are included; in a frequencyband of 10 MHz, 50 resource blocks are included; in a frequency band of15 MHz, 75 resource blocks are included; and in a frequency band of 20MHz, 100 resource blocks are included.

FIG. 6 illustrates a structural example of a symbol. The symbol includesa useful symbol which is a data portion and a cyclic prefix which is aguard interval. The cyclic prefix is a duplication of the last portionof the useful symbol, and is prefixed to the beginning of the usefulsymbol. As described above, there are two types of cyclic prefixes ofdifferent lengths, a normal cyclic prefix and an extended cyclic prefix.The duration of the normal cyclic prefix is 4.69 μsec while the durationof the extended cyclic prefix is 16.67 μsec, for example. The durationof the useful symbol stays the same regardless of using the normalprefix or the extended cyclic prefix.

For a normal subframe, the normal cyclic prefixes are generally usedwhile the extended cyclic prefixes are used for an MBSFN subframe. Themobile station 300 is configured to combine a delay wave signal having adelay time equal to or less than the cyclic prefix length with a directwave signal and other delay wave signals, and demodulate the combinedsignal. Compared to symbols with the normal cyclic prefixes, symbolswith the extended cyclic prefixes allow the mobile station 300 in theprocess of extracting MBMS data to use radio signals with larger delaytime (for example, radio signals transmitted from distant base stations)for the signal combination and demodulation. This leads to animprovement in reception quality of MBMS data transmitted in the MBSFNsubframe.

FIG. 7 illustrates a method of combining MBMS data signals. According tothe example of FIG. 7, a signal formed by superimposing MBMS datasignals transmitted from five base stations upon each other is receivedby the mobile station 300 as a signal formed by superimposing a directwave signal and four delay wave signals upon each other. Three out ofthe four delay wave signals have a delay time equal to or less than thecyclic prefix length, and the remaining one has a delay time exceedingthe cyclic prefix length. In this case, the mobile station 300 combinesthe direct wave signal and the three delay wave signals and demodulatesthe combined MBMS data signal.

FIG. 8 illustrates a frequency band setting example. The base stations200, 200 a, and 200 b may employ different frequency bands for radiocommunication, as described above. According to the example of FIG. 8,the base station 200 uses a frequency bandwidth of 10 MHz; the basestation 200 a uses a frequency bandwidth of 5 MHz; and the base station200 b uses a frequency bandwidth of 20 MHz, and all the base stations200, 200 a, and 200 b operate at the same center frequency. If thecenter frequency is fixed, a frequency band for radio communication isidentified by designating a bandwidth.

Note however that base stations may have different center frequencies.Further, some base stations may use a collection of multiple discretefrequency bands for radio communication. In these cases, a frequencyband is identified by designating both a center frequency and abandwidth. If band numbers are individually assigned to four 5-MHzblocks obtained by dividing the maximum frequency bandwidth of 20 MHz, afrequency band is identified by designating a band number.

FIG. 9 is a block diagram of an MCE. The MCE 100 includes a banddetermining unit 111, an MBSFN control unit 112, a scheduler 113, a bandinformation notifying unit 114, and an MBSFN control informationnotifying unit 115. Note that an integration of the band determiningunit 111 and the MBSFN control unit 112 represents an example of thecontrol unit 11 described above while the band information notifyingunit 114 is an example of the notifying unit 12.

The band determining unit 111 acquires, from each of the base stations200, 200 a, and 200 b, a band notification indicating a frequency bandused by (or available for) the base station for radio communication. Theband notification includes, for example, information indicating abandwidth or information indicating both a center frequency and abandwidth. Based on the acquired band notifications, the banddetermining unit 111 determines a frequency range common to all the basestations 200, 200 a, and 200 b as a frequency band available for MBSFNoperation. Subsequently, the band determining unit 111 notifies thedetermined frequency range to the MBSFN control unit 112.

When forming an MBSFN area, the MBSFN control unit 112 communicates withthe MME 41 to establish an MBSFN session. In addition, the MBSFN controlunit 112 notifies the MBSFN control information notifying unit 115 of alist of MBMS services to be provided. Further, referring to the amountof MBMS data to be transmitted, the MBSFN control unit 112 selects afrequency band to be used for the MBSFN session out of the availablefrequency band notified of by the band determining unit 111.Alternatively, the whole of the available frequency band may be alwaysselected as the frequency band for the MBSFN session. Subsequently, theMBSFN control unit 112 notifies the band information notifying unit 114of the selected frequency band.

In addition, the MBSFN control unit 112 acquires, from the base station200, an MBSFN request transmitted by the mobile station 300, andinstructs the scheduler 113 to schedule transmission of MBMS data for arequested MBMS service. Subsequently, the MBSFN control unit 112notifies the MBSFN control information notifying unit 115 of ascheduling result including information on allocated radio resources andan MCS.

The scheduler 113 schedules transmission of the MBMS data according tothe instruction of the MBSFN control unit 112. In the scheduling, thescheduler 113 allocates radio resources within the frequency bandselected by the MBSFN control unit 112 to transmission of the MBMS data.In addition, the scheduler 113 selects a predetermined MCS as one to beused for the transmission of the MBMS data. Alternatively, the scheduler113 may acquire, from the base station 200, channel quality informationindicating data reception quality measured at the mobile station 300 andselect an MCS according to the data reception quality.

The band information notifying unit 114 generates band informationindicating the frequency band selected by the MBSFN control unit 112,and transmits the band information to the base stations 200, 200 a, and200 b. The MBSFN control information notifying unit 115 generates MBSFNcontrol information indicating the list of MBMS services, and transmitsthe MBSFN control information to the base stations 200, 200 a, and 200b. In addition, the MBSFN control information notifying unit 115 alsogenerates MBSFN control information indicating a result of the MBMS datascheduling, and transmits the MBSFN control information to the basestations 200, 200 a, and 200 b and the MBMS gateway 42. Note that thetransmission cycle of the band information may be the same as, ordifferent from the transmission cycle of the MBSFN control information(for example, longer than the transmission cycle of the MBSFN controlinformation).

FIG. 10 is a block diagram of a base station. The base station 200includes an antenna 211; a radio receiving unit 212; a demodulation anddecoding unit 213; a quality information extracting unit 214; an MBSFNrequest extracting unit 215; a band setting unit 221; a scheduler 222,an MBSFN control unit 230; a control signal generating unit 241; anMBSFN control signal generating unit 242; a band control signalgenerating unit 243; a reference signal generating unit 244; a mappingunit 245; a coding and modulation unit 246; and a radio transmittingunit 247. The base stations 200 a and 200 b are also implemented usingthe same block architecture as the base station 200. Note that anintegration of the mapping unit 245, the coding and modulation unit 246,and the radio transmitting unit 247 represents an example of thetransmitting unit 21 described above while the MBSFN control unit 230 isan example of the control unit 22.

The antenna 211 receives a radio signal transmitted from the mobilestation 300 and outputs the radio signal to the radio receiving unit212. The antenna 211 also outputs a transmission signal acquired fromthe radio transmitting unit 247 as a radio signal. Note that, instead ofthe two-way transmitting and receiving antenna, a transmitting antennaand a receiving antenna may be separately provided in the base station200.

The radio receiving unit 212 carries out radio signal processing on thereceived signal acquired from the antenna 211 and converts thehigh-frequency radio signal into a baseband signal as a low-frequencysignal (down-conversion). For the radio signal processing, the radioreceiving unit 212 includes circuits such as a low noise amplifier(LNA), a quadrature demodulator, and an ADC (analog to digitalconverter).

The demodulation and decoding unit 213 demodulates anderror-correction-decodes the baseband signal acquired from the radioreceiving unit 212. The baseband signal is demodulated and decoded by amethod corresponding to a predetermined MCS or an MCS instructed by thescheduler 222. Extracted dedicated data of the mobile station 300 istransferred to the SAE gateway 43.

The quality information extracting unit 214 extracts channel qualityinformation transmitted by the mobile station 300. The channel qualityinformation indicates data reception quality measured at the mobilestation 300, and is, for example, a CQI (channel quality indicator)representing the data reception quality using a discrete value. Thechannel quality information is transmitted on a Physical Uplink ControlChannel (PUCCH). The quality information extracting unit 214 outputs theextracted channel quality information to the scheduler 222.

The MBSFN request extracting unit 215 extracts an MBSFN requesttransmitted by the mobile station 300. The MBSFN request includesinformation indicating an MBMS service desired by the mobile station 300and is transmitted on a Physical Uplink Shared Channel (PUSCH). TheMBSFN request extracting unit 215 outputs the extracted MBSFN request tothe MBSFN control unit 230.

The band setting unit 221 sets a frequency band to be used for radiocommunication between the base station 200 and the mobile station 300.According to a setting made by an operator, the band setting unit 221sets the frequency band at the start of operation of the base station200. In addition, when a predetermined condition (for example, acondition for a period of time) is satisfied, the band setting unit 221changes the frequency band to be used. The band setting unit 221notifies the MBSFN control unit 230 of a frequency band in current use.

The scheduler 222 schedules transmission and reception of dedicated dataof the mobile station 300. In the scheduling, the scheduler 222 refersto the channel quality information acquired from the quality informationextracting unit 214 and a result of MBMS data scheduling notified of bythe MBSFN control unit 230. The scheduling includes allocation of radioresources and selection of an MCS. For dedicated data directed to themobile station 300, radio resources other than the MBSFN subframe areallocated. Based on a result of the dedicated data scheduling, thescheduler 222 controls signal processing of the radio receiving unit212, the demodulation and decoding unit 213, the coding and modulationunit 246, and the radio transmitting unit 247. The scheduler 222 alsonotifies the control signal generating unit 241 of the result of thededicated data scheduling.

The MBSFN control unit 230 generates a band notification indicating thefrequency band set by the band setting unit 221 and transmits the bandnotification to the MCE 100. The MBSFN control unit 230 also transfersthe MBSFN request extracted by the MBSFN request extracting unit 215 tothe MCE 100. In addition, the MBSFN control unit 230 outputs MBSFNcontrol information to the MBSFN control signal generating unit 242after receiving it from the MCE 100. Further, the MBSFN control unit 230outputs band information to the band control signal generating unit 243after receiving it from the MCE 100. Based on the received bandinformation and MBSFN control information, the MBSFN control unit 230controls a frequency band and radio resources used for the MBSFNsubframe, and notifies the scheduler 222 of the result of MBMS datascheduling.

Based on the result of the dedicated data scheduling notified of by thescheduler 222, the control signal generating unit 241 generates adedicated transmission control signal to be transmitted on a PhysicalDownlink Control Channel (PDCCH). The dedicated transmission controlsignal includes information indicating radio resources and an MCS usedfor dedicated data transmission. The control signal generating unit 241outputs the generated dedicated transmission control signal to themapping unit 245.

Based on the MBSFN control information received from the MCE 100, theMBSFN control signal generating unit 242 generates an MBSFN controlsignal to be transmitted on a PMCH (Physical Multicast Channel). TheMBSFN control signal includes information indicating the list of MBMSservices and information indicating the radio resources and the MCS tobe used for MBMS data transmission. The MBSFN control signal generatingunit 242 outputs the generated MBSFN control signal to the mapping unit245. Note that the following two channels are mapped to the PMCH: anMCCH (Multicast Control Channel) which is a logical channel fortransmitting MBSFN control information; and an MTCH (Multicast TrafficChannel) which is a logical channel for transmitting MBMS data.

Based on the band information received from the MCE 100, the bandcontrol signal generating unit 243 generates a band control signal to betransmitted on the PMCH (MCCH), and then outputs the band control signalto the mapping unit 245.

The reference signal generating unit 244 generates reference signalswhich are known pilot signals, and then outputs the reference signals tothe mapping unit 245.

The mapping unit 245 maps, to a downlink radio frame, MBMS data receivedfrom the MBMS gateway 42 and dedicated data received from the SAEgateway 43. To the downlink radio frame, the mapping unit 245 also mapsthe signals acquired from the control signal generating unit 241, theMBSFN control signal generating unit 242, the band control signalgenerating unit 243, and the reference signal generating unit 244.Subsequently, the mapping unit 245 outputs a transmission signal of thedownlink radio frame to the coding and modulation unit 246.

The coding and modulation unit 246 error-correction-codes and modulatesthe transmission signal acquired from the mapping unit 245, and outputsa resultant transmission signal to the radio transmitting unit 247. Forthe coding and modulation, a predetermined MCS or an MCS instructed bythe scheduler 222 is used.

The radio transmitting unit 247 carries out radio signal processing onthe transmission signal acquired from the coding and modulation unit 246to thereby convert the low-frequency baseband signal into ahigh-frequency radio signal (up-conversion). For the radio signalprocessing, the radio transmitting unit 247 includes circuits such as aDAC (digital to analog converter), a quadrature modulator, a poweramplifier, and so on.

FIG. 11 is a block diagram of an MBSFN control unit of a base station.The MBSFN control unit 230 includes an MBSFN request processing unit231, an MBSFN control information processing unit 232, and an MBSFN bandcontrol unit 233.

The MBSFN request processing unit 231 acquires, from the MBSFN requestextracting unit 215, the MBSFN request transmitted by the mobile station300 and then outputs the MBSFN request to the MBSFN control informationprocessing unit 232.

The MBSFN control information processing unit 232 acquires the MBSFNcontrol information transmitted by the MCE 100. Subsequently, based onthe MBSFN scheduling result indicated by the MBSFN control informationand an MBSFN frequency band notified of by the MBSFN band control unit233, the MBSFN control information processing unit 232 configuressettings for an MBSFN subframe, a frequency band used for the MBSFNsubframe, the PMCH, and the like. In addition, the MBSFN controlinformation processing unit 232 notifies the scheduler 222 of the resultof the MBMS data scheduling, and outputs the MBSFN control informationto the MBSFN control single generating unit 242.

The MBSFN band control unit 233 transmits a band notification indicatinga frequency band used by the base station 200 to the MCE 100 at apredetermined timing. The predetermined timing may be the time when anMBSFN session is started and the time when a change is made to thefrequency band used by the base station 200. In addition, the MBSFN bandcontrol unit 233 acquires band information transmitted by the MCE 100,then notifies the MBSFN control information processing unit 232 of theMBSFN frequency band indicated by the band information, and outputs theband information to the band control signal generating unit 243.

FIG. 12 is a block diagram of a mobile station. The mobile station 300includes an antenna 311; a radio receiving unit 312; a demodulation anddecoding unit 313; a control signal extracting unit 314; an MBSFNcontrol signal extracting unit 315; a band control signal extractingunit 316; a reference signal extracting unit 317; a terminal controlunit 321; an MBSFN control unit 322; a quality measuring unit 323; anMBSFN request generating unit 331; a quality information generating unit332; a coding and modulation unit 333; and a radio transmitting unit334. Note that the MBSFN control unit 322 is an example of the controlunit 31 described above.

The antenna 311 receives a signal corresponding to radio signalstransmitted by multiple base stations including the base stations 200,200 a, and 200 b, and outputs the received signal to the radio receivingunit 312. The antenna 311 also wirelessly outputs a transmission signalacquired from the radio transmitting unit 334. Note that, instead of thetwo-way transmitting and receiving antenna, a transmitting antenna and areceiving antenna may be separately provided in the mobile station 300.

The radio receiving unit 312 carries out radio signal processing on thereceived signal acquired from the antenna 311 and downconverts the radiosignal into a baseband signal. For the radio signal processing, theradio receiving unit 312 includes circuits such as an LNA, a quadraturedemodulator, and an ADC.

The demodulation and decoding unit 313 demodulates anderror-correction-decodes the baseband signal acquired from the radioreceiving unit 312. The baseband signal is demodulated and decoded by amethod corresponding to a predetermined MCS or an MCS instructed by theterminal control unit 321. Extracted dedicated data and MBMS data aretransferred to a data processing unit of an upper layer (notillustrated), such as a processor. The case is considered that themobile station 300 receives MBMS data transmitted by MBSFN. A signalreceived by the mobile station 300 is formed by superimposing MBMS datasignals transmitted from multiple base stations upon each other. Thereceived signal appears to the mobile station 300 as superposition ofadvance and delay waves. The demodulation and decoding unit 313 extractsdelay wave signals each having a delay time equal to or less than thecyclic prefix length and combines the delay wave signals with a directwave signal, and then demodulates and decodes the combined signal.

The control signal extracting unit 314 extracts the dedicatedtransmission control signal transmitted on the PDCCH. The dedicatedtransmission control signal includes information indicating radioresources and an MCS used for dedicated data transmission, as describedabove. The control signal extracting unit 314 outputs the extracteddedicated transmission control signal to the terminal control unit 321.

The MBSFN control signal extracting unit 315 extracts the MBSFN controlsignal transmitted on the PMCH with the MCCH mapped thereto. The MBSFNcontrol signal includes information indicating a list of MBMS servicesand information indicating radio resources and an MCS used for MBMS datatransmission, as described above. The MBSFN control signal extractingunit 315 outputs the extracted MBSFN control signal to the MBSFN controlunit 322.

The band control signal extracting unit 316 extracts the band controlsignal transmitted on the PMCH with the MCCH mapped thereto, and outputsthe extracted band control signal to the MBSFN control unit 322.

The reference signal extracting unit 317 extracts reference signalsincluded in a downlink radio frame and outputs the extracted referencesignals to the quality measuring unit 323.

The terminal control unit 321 controls transmission and reception ofdedicated data based on the dedicated transmission control signalextracted by the control signal extracting unit 314. In addition, theterminal control unit 321 controls reception of MBMS data based on anotification from the MBSFN control unit 322. The terminal control unit321 controls signal processing of the radio receiving unit 312, thedemodulation and decoding unit 313, the coding and modulation unit 333,and the radio transmitting unit 334.

The MBSFN control unit 322 instructs the MBSFN request generating unit331 to transmit an MBSFN request in order to start receiving MBMS datain response to, for example, a user's operation. In addition, the MBSFNcontrol unit 322 acquires the MBSFN control signal extracted by theMBSFN control signal extracting unit 315 and the band control signalextracted by the band control signal extracting unit 316. Then, theMBSFN control unit 322 determines a frequency band and a timing forreceiving an MBMS data signal and an MCS applied to the MBMS data, andnotifies the terminal control unit 321 of the determined information.

The quality measuring unit 323 measures data reception quality, such asa CIR (Carrier to Interference Ratio), or radio channel quality, usingthe reference signals extracted by the reference signal extracting unit317. Subsequently, the quality measuring unit 323 outputs themeasurement result to the quality information generating unit 332 andalso feeds the measurement result back to the reference signalextracting unit 317 in order to improve the accuracy of reference signalextraction.

The MBSFN request generating unit 331 generates an MBSFN requestindicating an MBMS service desired to be used (a type of MBMS datadesired to be received) in response to an instruction from the MBSFNcontrol unit 322. The MBMS service asked for by the MBSFN request isselected from the list of MBMS services transmitted by the base station200. The MBSFN request generating unit 331 outputs the generated MBSFNrequest to the coding and modulation unit 333.

The quality information generating unit 332 generates channel qualityinformation indicating the data reception quality (or the radio channelquality) measured by the quality measuring unit 323. As the channelquality information, the CQI, for example, is used. The qualityinformation generating unit 332 outputs the generated channel qualityinformation to the coding and modulation unit 333.

The coding and modulation unit 333 error-correction-codes and modulatesdedicated data to be transmitted on the PUSCH, the MBSFN requestacquired from the MBSFN request generating unit 331, and the channelquality information acquired from the quality information generatingunit 332, and then outputs a resultant transmission signal to the radiotransmitting unit 334. For the coding and modulation, a predeterminedMCS or an MCS instructed by the terminal control unit 321 is used.

The radio transmitting unit 334 carries out radio signal processing onthe transmission signal acquired from the coding and modulation unit 333to thereby upconvert the baseband signal into a radio signal. For theradio signal processing, the radio transmitting unit 334 includescircuits such as a DAC, a quadratuer modulator, a power amplifier, andso on.

FIG. 13 is a flowchart illustrating band control exercised by an MCE.The band control of FIG. 13 is described next according to the stepnumbers in the flowchart.

(Step S11) The band determining unit 111 determines whether to havereceived a band notification. For example, at the start of an MBSFNsession, the band determining unit 111 determines whether to havereceived band notifications from all base stations belonging to acorresponding MBSFN area. On the other hand, after the start of theMBSFN operation, the band determining unit 111 determines whether tohave received a band notification from one of the base stations of theMBSFN area. When the band determining unit 111 has received a bandnotification, the process moves to step S13. If not, the process movesto step S12.

(Step S12) The band determining unit 111 determines whether there is achange to the group of the base stations belonging to the MBSFN area(for example, whether there is an increase or a decrease in the basestations for carrying out MBSFN transmission). If there is a change tothe group of the base stations, the process moves to step S13. If not,the process moves to step S14. Note that addition and deletion of basestations for MBSFN transmission are determined by the MCE 100 accordingto the usage situation of MBMS services.

(Step S13) Based on band notifications corrected from the base stationsof the MBSFN area, the band determining unit 111 determines a commonrange within an entire frequency band used by the base stations forradio communication as a frequency band available for MBSFN. Note thatwhen a base station belonging to the MBSFN area changes its frequencyband for radio communication and when there is a change to the group ofthe base stations belonging to the MBSFN area, the frequency bandavailable for MBSFN may also be changed.

(Step S14) The MBSFN control unit 112 selects a frequency band to beused for MBSFN out of the frequency band determined in step S13 (or afrequency band previously determined to be available for MBSFN). Forexample, the MBSFN control unit 112 selects a minimum frequencybandwidth to hold MBMS data to be transmitted. Note however that thewhole of the available frequency band may always be selected as thefrequency band to be used for MBSFN.

(Step S15) The band information notifying unit 114 generates bandinformation indicating the frequency band selected in step S14, andtransmits the band information to the base stations belonging to theMBSFN area. Note that the interval of transmitting the band informationmay be longer than that of MBSFN control information regardingscheduling of MBMS data transmission.

FIG. 14 is a flowchart illustrating band control exercised by a basestation. The following is the case where the base station 200 exercisesthe band control. The band control of FIG. 14 is described nextaccording to the step numbers in the flowchart.

(Step S21) The MBSFN control unit 230 determines whether it is when anMBSFN session (i.e., MBSFN operation) is started. If it is when an MBSFNsession is started, the process moves to step S23. If not, the processmoves to step S22.

(Step S22) The MBSFN control unit 230 determines whether there is achange to the frequency band that the base station 200 uses for radiocommunication with the mobile station 300. If there is a change, theprocess moves to step S23. If not, the process moves to step S24.

(Step S23) The MBSFN control unit 230 generates a band notificationindicating a frequency band that the band station 200 uses, andtransmits the band notification to the MCE 100.

(Step S24) The MBSFN control unit 230 receives, from the MCE 100, bandinformation indicating a frequency band to be used for MBSFN.

(Step S25) Based on the band information received in step S24, the bandcontrol signal generating unit 243 generates a band control signalindicating the frequency band to be used for MBSFN. After beingsubjected to the processing by the mapping unit 245 and the coding andmodulation unit 246, the band control signal is transmitted, to themobile station 300, by the radio transmitting unit 247 on the PMCH(MCCH) in an MBSFN subframe.

(Step S26) The MBSFN control unit 230 uses the band information receivedin step S24 to thereby control transmission of MBMS data. For example,the MBSFN control unit 230 controls, in the MBSFN subframe, an MBMS datasignal to be output in a range within the frequency band indicated bythe band information.

FIG. 15 is a flowchart illustrating band control exercised by a mobilestation. The band control of FIG. 15 is described next according to thestep numbers in the flowchart.

(Step S31) The MBSFN control unit 322 determines whether an MBSFNrequest has already been transmitted to the base station 200. If anMBSFN request has already been transmitted, the process moves to stepS32. If not, the process is ended.

(Step S32) The band control signal extracting unit 316 extracts a bandcontrol signal transmitted in an MBSFN subframe by the base station 200.Note that the band control signal extracting unit 316 has been notifiedof the location of the MBSFN subframe with, for example, broadcastinformation transmitted by the base station 200.

(Step S33) The MBSFN control unit 322 identifies a frequency band to beused for MBSFN based on the band control signal extracted in step S32.The terminal control unit 321 sets the frequency band to be used forMBSFN.

(Step S34) Based on the frequency band set in step S33, the terminalcontrol unit 321 controls reception of MBMS data. For example, theterminal control unit 321 extracts a radio signal in the set frequencyband from the MBSFN subframe.

FIG. 16 is a sequence diagram illustrating a flow of communicationaccording to the second embodiment. The flow of communication of FIG. 16is described next according to the step numbers in the sequence diagram.

(Step S41) When starting MBSFN operation, the MME 41 transmits a requestfor starting an MBSFN session to the MCE 100.

(Step S42) The MCE 100 determines to be ready to start MBSFN control,and transmits a response to the MBSFN session start request to the MME41.

(Step S43) The MCE 100 selects base stations belonging to the MBSFNarea, and transmits a request for starting an MBSFN session to each ofthe selected base stations (the base stations 200, 200 a, and . . . ).Note that base stations other than the base stations 200 and 200 a areomitted from FIG. 16.

(Step S44) Each of the base stations 200, 200 a, and . . . determines tobe ready to start MBSFN transmission, and transmits a response to theMBSFN session start request to the MCE 100.

(Step S45) Each of the base stations 200, 200 a, and . . . transmits, tothe MCE 100, a band notification indicating a frequency band that thebase station uses for radio communication.

(Step S46) Based on the band notifications received in step S45, the MCE100 determines a frequency band common to all the base stations 200, 200a, and . . . .

(Step S47) The MCE 100 transmits an MBSFN session start notificationindicating start of MBSFN transmission to each of the base stations 200,200 a, and . . . .

(Step S48) The MCE 100 transmits, to each of the base stations 200, 200a, and . . . , MBSFN control information indicating a list of MBMSservices available for the mobile station 300. The base station 200transmits an MBSFN control signal indicating the list of MBMS servicesto the mobile station 300 on the PMCH (MCCH). In addition, the MCE 100also transmits the MBSFN control information to the MBMS gateway 42.

FIG. 17 is a sequence diagram (continuing from FIG. 16) illustrating theflow of communication according to the second embodiment.

(Step S51) The mobile station 300 selects an MBMS service to use fromthe list indicated by the MBSFN control signal received in step S48, andtransmits an MBSFN request to the base station 200 on the PUSCH. Thebase station 200 transfers the MBSFN request to the MCE 100.

(Step S52) The MCE 100 selects a frequency band to be used for MBSFNfrom the frequency band determined in step S46.

(Step S53) The MCE 100 transmits, to each of the base stations 200, 200a, and . . . , band information indicating the frequency band selectedin step S52 and MBSFN control information regarding scheduling of MBMSdata transmission. The base station 200 transmits, to the mobile station300, a band control signal and an MBSFN control signal on the PMCH(MCCH). Based on the received band control signal and MBSFN controlsignal, the mobile station 300 configures settings for receiving MBMSdata. In addition, the MCE 100 also transmits the MBSFN controlinformation to the MBMS gateway 42. Note that the MBSFN controlinformation and the band information may be transmitted at differenttimes.

(Step S54) The MBMS gateway 42 transmits MBMS data to each of the basestations 200, 200 a, and . . . . The base stations 200, 200 a, and . . .individually transmit, to the mobile station 300, an MBMS data signal onthe PMCH (MTCH). The mobile station 300 combines the MBMS data signalstransmitted by the base stations 200, 200 a, and . . . , and demodulatesand decodes the combined signal.

Note that when there is a change to the frequency band of a base stationbelonging to the MBSFN area, the same processing as in theabove-described steps S45 and S46 is repeated to thereby recalculate afrequency band available for MBSFN. In addition, when the MCE 100 addsor deletes a base station for participating in MBSFN transmission, thesame processing as in step S46 is repeated to thereby recalculate afrequency band available for MBSFN. Upon recalculation of the availablefrequency band, the processing of steps S52 and S53 is executed based onthe changed frequency band.

FIG. 18 illustrates a first example of how to set an MBSFN band. Thisexample depicts the case where base stations belonging to an MBSFN areahave frequency bands with the same center frequency. For example, thebase station 200 operates in a frequency band of 10 MHz, the basestation 200 a operates in a frequency band of 5 MHz, and the basestation 200 b operates in a frequency band of 20 MHz.

In this case, a band notification transmitted by the base station 200 tothe MCE 100 indicates that the base station 200 uses a bandwidth of 10MHz. Similarly, a band notification transmitted by the base station 200a to the MCE 100 indicates that the base station 200 a uses a bandwidthof 5 MHz while a band notification transmitted by the base station 200 bto the MCE 100 indicates that the base station 200 b uses a bandwidth of20 MHz. Subsequently, the MCE 100 determines, for example, the minimumbandwidth of 5 MHz among the bandwidths of 5 MHz, 10 MHz, and 20 MHz asa frequency band to be used for MBSFN. Then, the MCE 100 transmits bandinformation indicating the determined bandwidth of 5 MHz to each of thebase stations 200, 200 a, and 200 b. The base stations 200, 200 a, and200 b individually set the 5 MHz frequency band around the centerfrequency as the frequency band to be used for MBSFN.

FIG. 19 illustrates a second example of how to set an MBSFN band. Thisexample depicts the case where base stations belonging to an MBSFN areahave frequency bands with different center frequencies. For example, thebase station 200 operates in a continuous frequency band of 10 MHz whilethe base station 200 a operates in two discrete frequency bands of 5 MHz(10 MHz bandwidth in total). In addition, the base station 200 boperates in a continuous frequency band of 20 MHz.

In this case, a band notification transmitted by the base station 200 tothe MCE 100 indicates the bandwidth that the base station 200 uses (10MHz) and its center frequency. A band notification transmitted by thebase station 200 a to the MCE 100 indicates the two bandwidths that thebase station 200 a uses (5 MHz×2) and their individual centerfrequencies. A band notification transmitted by the base station 200 bto the MCE 100 indicates the bandwidth that the base station 200 b uses(20 MHz) and its center frequency. Subsequently, the MCE 100 selects,for example, a 5 MHz frequency band commonly used by the base stations200, 200 a, and 200 b as a frequency band to be used for MBSFN. Then,the MCE 100 transmits band information indicating the selected 5MHz-width frequency band and its center frequency to each of the basestations 200, 200 a, and 200 b. The base stations 200, 200 a, and 200 bindividually set the frequency band indicated by the band information asthe frequency band to be used for MBSFN.

Note that, in the description above, the MCE 100 transmits, to each ofthe base stations 200, 200 a, and 200 b, the band information separatelyfrom the MBSFN control information. However, the band information may betransmitted as part of the MBSFN control information, instead. Inaddition, in the case of transmitting MBMS data with real-timetransmission restrictions by MBSFN, the MCE 100 may select a frequencyband to be used for MBSFN in consideration of a needed transmission rateof the MBMS data.

FIG. 20 is a block diagram illustrating a first modification example ofan MCE according to a first modification. An MCE 100 a of FIG. 20 may beused in place of the MCE 100. The MCE 100 a includes an MBSFN controlinformation notifying unit 115 a, in place of the band informationnotifying unit 114 and the MBSFN control information notifying unit 115of the MCE 100.

In response to an instruction from the MBSFN control unit 112, the MBSFNcontrol information notifying unit 115 a generates MBSFN controlinformation, which is then transmitted to the base stations 200, 200 a,and 200 b or the MBMS gateway 42. The MBSFN control information mayinclude band information indicating a frequency band to be used forMBSFN. Note that in place of the band determining unit 111, the MBSFNcontrol unit 112, and the MBSFN control information notifying unit 115a, a control unit assuming all the functions of these units may beprovided in the MCE 100 a.

FIG. 21 is a block diagram illustrating a second modification example ofan MCE according to a second modification. An MCE 100 b of FIG. 21 maybe used in place of the MCE 100. The MCE 100 b includes a banddetermining unit 111 b in place of the band determining unit 111 of theMCE 100. The band determining unit 111 b receives, from the MME 41,information indicating a needed transmission rate of MBMS data with aneed for real-time transmission. For example, between steps S41 and S42described above, the band determining unit 111 b receives informationindicating the needed transmission rate. Subsequently, the banddetermining unit 111 b calculates a minimum bandwidth to satisfy theneeded transmission rate, and notifies the MBSFN control unit 112 of theminimum bandwidth. The MBSFN control unit 112 reserves, for MBSFN, afrequency band with at least the bandwidth notified of by the banddetermining unit 111 b.

Note that, in the description above, each of the base stations 200, 200a, and 200 b is able to use a frequency band up to 20 MHz for downlinkradio communication on the basis of LTE. However, on the basis of LTE-A,each of the base stations 200, 200 a, and 200 b may use up to five20-MHz frequency bands for downlink radio communication. In LTE-A, eachfrequency band of 20 MHz or less is called a component carrier (CC).

FIG. 22 illustrates a configuration example of component carriers. Thebase stations 200, 200 a, and 200 b may individually use up to fivecomponent carriers (CCs #1 to #5) for downlink radio communication. Abandwidth of each component carrier is selected from among, for example,1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. Note that CCs #1 to#5 may have different bandwidths. Each of CCs #1 to #5 transmits a radioframe as illustrated in FIG. 4. The base stations 200, 200 a, and 200 bcontrol radio resource allocation for each component carrier.

The base stations 200, 200 a, 200 b respectively aggregate multiplecomponent carriers for radio communication with the mobile station 300(i.e., use multiple component carriers at the same time). This enablesradio communication using a wider frequency band than the frequency bandof a single component carrier. All CCs #1 to #5 may be provided in asingle frequency band, such as an 800 MHz band, a 2.0 GHz band, or a 3.5GHz band, or may be provided separately in multiple different frequencybands. Aggregating multiple component carriers is sometimes referred toas the “carrier aggregation”. Carrier aggregation of component carriersbelonging to different frequency bands is sometimes referred to as the“spectrum aggregation”.

According to the above-described method of setting an MBSFN frequencyband, the MBSFN frequency band may be provided within a single componentcarrier, or over multiple component carriers. For example, each of thebase stations 200, 200 a, and 200 b transmits a band notificationindicating bandwidths of the individual CCs #1 to #5 to the MCE 100. TheMCE 100 selects a component carrier used for MBSFN (for example, alowest frequency component carrier), and then selects a frequency bandbased on the bandwidths of the selected component carrier of theindividual base stations 200, 200 a, and 200 b. Alternatively, the MCE100 selects one or more component carriers and a frequency band used forMBSFN based on the bandwidths of CCs #1 to #5 of the base stations 200,200 a, and 200 b.

With the mobile communication system according to the second embodimentdescribed above, the MCE 100 recognizes setting statuses of radiocommunication frequency bands used by individual base stations in theMBSFN area to be thereby able to select an appropriate frequency bandfor MBSFN. The appropriate selection of the frequency band for MBSFNreduces the possibility of rendering some base stations in the MBSFNarea incapable of transmitting part of MBMS data due to lack of radioresources. As a result, it is possible to reduce loss of quality in MBMSdata reception at the mobile station 300.

In addition, as compared to the case of selecting the frequency band tobe used for MBSFN on the basis of using the smallest possible bandwidth(for example, 1.4 MHz) set for the base stations in the MBSFN area, thesecond embodiment prevents the bandwidth of the frequency band to beused for MBSFN from becoming excessively small and, thus, ensures theefficient use of radio resources of the individual base stations. Inaddition, the MCE 100 is able to provide a dynamic update of thefrequency band used for MBSFN when a change is made to the frequencyband of a base station belonging to the MBSFN area or when there is achange to the group of the base stations belonging to the MBSFN area.

Third Embodiment

A third embodiment is described next. Hereinafter, the discussion willbe focused on differences from the second embodiment while theexplanations of the components common to the second embodiment areomitted. A mobile communication system of the third embodiment isdifferent from that of the second embodiment in a path used to transmitband notifications from base stations to an MCE.

The mobile communication system of the third embodiment may be achievedusing the same system configuration as that of the mobile communicationsystem of the second embodiment illustrated in FIG. 2. Note howeverthat, in the third embodiment, an MME 400 described below is used inplace of the MME 41. An MCE, base stations, and a mobile station of thethird embodiment are implemented using the same block architectures asthe individual counterparts of the second embodiment, illustrated inFIGS. 9 to 12. In the following description, the MCE, base stations, andmobile station of the third embodiment are denoted by the same referencenumerals in the second embodiment.

FIG. 23 is a block diagram of an MME. The MME 400 includes an MBSFNsession control unit 411 and a channel control unit 412. The MBSFNsession control unit 411 controls start of an MBSFN session. The MBSFNsession control unit 411 transmits an MBSFN session start request to theMCE 100, and subsequently receives an MBSFN session start response fromthe MCE 100. The channel control unit 412 receives a band notificationfrom each of the base stations 200, 200 a, and 200 b and, then,transfers the band notifications to the MCE 100.

FIG. 24 is a sequence diagram illustrating a flow of communicationaccording to the third embodiment. Among steps S61 to S69 of FIG. 24,the operations of steps S61 to S64, S68, and S69 are the same as thoseof steps S41 to S44, S47, and S48 of FIG. 16.

(Step S65) Each of the base stations 200, 200 a, and . . . transmits, tothe MME 400 without the MCE 100, a band notification indicating afrequency band that the base station uses for radio communication.

(Step S66) The MME 400 transfers the band notifications received fromthe base stations 200, 200 a, and . . . to the MCE 100. Note that in thecase of the start of an MBSFN session, the MME 400 may transfer each ofthe band notifications received from the base stations 200, 200 a, and .. . to the MCE 100, or transfer collectively band notifications of twoor more base stations to the MCE 100.

(Step S67) Based on the band notifications received from the MME 400 instep S66, the MCE 100 determines a frequency band common to all the basestations 200, 200 a, and . . . .

Note that in the case where a change is made to the frequency band of abase station belonging to the MBSFN area, a band notification istransferred via the MME 400 to the MCE 100, which subsequentlyrecalculates a frequency band available for MBSFN.

According to such a mobile communication system of the third embodiment,the same effect as in the second embodiment may be achieved. Inaddition, according to the third embodiment, the MCE 100 controls MBSFNin efficient cooperation with the MME 400 having the channel controlfunction.

According to the above-described radio communication system and methodtherefor, communication controller, and base station, it is possible toreduce loss of data reception quality in the case where data with commoncontent is transmitted from two or more base stations.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A radio communication system comprising: acommunication control apparatus; a plurality of base stations; and aradio receiving apparatus, in which radio communication system, two ormore base stations among the plurality of base stations transmit datawith common content to the radio receiving apparatus at a frequencycommon to the two or more base stations, wherein each of the two or morebase stations includes a first control unit for notifying thecommunication control apparatus of information on a frequency band thatthe base station uses for radio communication, and controllingtransmission of the data with common content based on information on afrequency band notified of by the communication control apparatus, andthe communication control apparatus includes a second control unit forselecting a frequency band from a frequency range commonly included inthe frequency bands notified of by the two or more base stations, and anotifying unit for notifying the two or more base stations of theinformation on the selected frequency band.
 2. The radio communicationsystem according to claim 1, wherein the information on the selectedfrequency band includes information indicating a bandwidth of theselected frequency band or information indicating a center frequency andthe bandwidth of the selected frequency band.
 3. The radio communicationsystem according to claim 1, wherein the second control unit calculatesa frequency band available for transmission of the data with commoncontent based on the information of the frequency bands notified of bythe two or more base stations, and selects a frequency band based on theavailable frequency band and a transmission status of the data withcommon content.
 4. The radio communication system according to claim 3,wherein when a change is made to the frequency band that the basestation uses for radio communication, the first control unit of the basestation notifies the communication control apparatus of information onthe changed frequency band, and the second control unit recalculates theavailable frequency band based on the information on the changedfrequency band.
 5. The radio communication system according to claim 3,wherein the second control unit recalculates the available frequencyband when there is a change in, among the plurality of base stations,the two or more base stations transmitting the data with common content.6. The radio communication system according to claim 1, wherein thefirst control unit notifies the radio receiving apparatus of theinformation on the selected frequency band notified of by thecommunication control apparatus, and the radio receiving apparatusincludes a third control unit for controlling reception of the data withcommon content from the two or more base stations based on theinformation on the selected frequency band.
 7. The radio communicationsystem according to claim 1, wherein the communication control apparatusis an apparatus implemented on at least one of the plurality of basestations.
 8. A communication control apparatus comprising: a controlunit for acquiring, from each of two or more base stations transmittingdata with common content at a frequency common to the two or more basestations, information on a frequency band that the base station uses forradio communication, and selecting a frequency band from a frequencyrange commonly included in the frequency bands acquired from the two ormore base stations; and a notifying unit for notifying the two or morebase stations of information on the frequency band selected by thecontrol unit.
 9. A base station used in a radio communication systemincluding a communication control apparatus; a plurality of basestations; and a radio receiving apparatus, in which radio communicationsystem, two or more base stations among the plurality of base stationstransmit data with common content to the radio receiving apparatus at afrequency common to the two or more base stations, the base stationcomprising: a transmitting unit for transmitting the data with commoncontent according to an instruction from the communication controlapparatus; and a control unit for notifying the communication controlapparatus of information on a frequency band that the base station usesfor radio communication, acquiring information on a frequency band thatthe communication control apparatus selects from a frequency rangecommonly included in the frequency bands notified of by the two or morebase stations, and controlling the transmitting unit with respect to thetransmission of the data with common content based on the information onthe frequency band selected by the communication control apparatus. 10.A radio communication method for a radio communication system includinga communication control apparatus; a plurality of base stations; and aradio receiving apparatus, in which radio communication system, two ormore base stations among the plurality of base stations transmit datawith common content to the radio receiving apparatus at a frequencycommon to the two or more base stations, the radio communication methodcomprising: notifying, by each of the two or more base stations, thecommunication control apparatus of information on a frequency band thatthe base station uses for radio communication; selecting, by thecommunication control apparatus, a frequency band from a frequency rangecommonly included in the frequency bands notified of by the two or morebase stations, and notifying the two or more base stations ofinformation on the selected frequency band; and transmitting, by the twoor more base stations, the data with common content based on theinformation on the selected frequency band notified of by thecommunication control apparatus.